The results of spectroscopic measurements on the atmospheric column water vapour content over the Issyk-Kul region (Kirghizia) and near Hevana (Cuba) are presented. The statistical analysis shows that the periodic variations of the water vapour content are due to planetary waves with different wave numbers. The observations indicate that air masses have the same phases at least in the lower and middle troposphere. In the tropical zone the day-time variations of the water vapour content have a twelve hour periodicity with a minimum about the local noon.